The vertebrae in birds are mostly

Options

A. Acoelous
B. Heterocoelous
C. Amphicoelous
D. Procoelous

Answer

To answer the question "The vertebrae in birds are mostly," we will analyze the options provided and determine the correct answer step by step.

### Step-by-Step Solution:

1. **Understanding the Options**:
- The options given are:
- A) Acellus
- B) Heterocellus
- C) Amphicellus
- D) Procellus

2. **Analyzing Acellus**:
- Acellus vertebrae are flat on both the anterior and posterior sides of the centrum.
- This type of vertebrae is typically found in humans.

3. **Analyzing Heterocellus**:
- Heterocellus vertebrae have a saddle-shaped centrum.
- This shape allows for high flexibility, which is essential for the movement of a bird's neck.
- Given that birds require significant neck flexibility for various activities, this type of vertebrae is characteristic of birds.

4. **Analyzing Amphicellus**:
- Amphicellus vertebrae have cavities on both sides of the centrum.
- This type is commonly found in fish, not in birds.

5. **Analyzing Procellus**:
- Procellus vertebrae have a concave anterior end and a convex posterior end.
- This type is typically found in reptiles.

6. **Conclusion**:
- Based on the analysis, the vertebrae in birds are mostly **heterocellus** due to their saddle-shaped structure that allows for greater flexibility in the neck.

### Final Answer:
The vertebrae in birds are mostly **heterocellus**.

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